This invention relates generally to the field of circular saws, and more particularly to the field of circular saws which move relative to the workpiece being cut. Even more particularly, the invention relates to large circular saws moved hydraulically in a pivoting and traversing motion relative to a workpiece receiving cradle, such as saws used in the logging industry to cut trees into short wood lengths.
There are numerous steps in bringing a tree from the forest to a mill for final processing into lumber, pulp, etc. Each tree is felled, delimbed and transported by truck to the mill. For some uses the logs are cut into short sections, usually from 4 to 8 feet in length. Cutting short wood, as it is known, may occur in the field prior to loading on the trucks, at intermediary wood yards for loading the wood onto trucks or rail cars, or at the mill itself. For increased speed, a number of logs are cut in a single pass with a large saw, rather than being cut individually. A motorized piece of heavy equipment known as a loader picks up several logs with a large grapple--a pincer type device--and loads them into the cradle or bunk of the saw. When the cradle is filled to the maximum allowable height, a hydraulically operated butt board evens the ends, the logs are cut by the saw and the short wood is removed by the grapple and placed on the truck or into train cars. The loader then uses the grapple to grasp and slide the remaining log lengths forward past the saw and the process is repeated.
There are three standard saws in use for this type of operation. The first type consists of an elongated chain saw typically 4 to 5 feet in length which pivots from a recessed vertical position just to one side of the cradle down to a horizontal position during the cutting stroke. The recessed position allows the logs to be moved in the cradle and protects the saw blade from damage. The other two types use circular saw blades of up to 5 feet in diameter. In one type, the blade is pivoted from a recessed vertical position down into the cradle, in a manner similar to the chain saw type. In the other type, the blade is mounted on a multi-jointed elbow-like arm which brings the blade from the recessed position across the cradle.
The circular saws are more powerful than the chain saw type, and the chain saw type cannot be used in northern locations on frozen trees. Additionally, the chain saw types are easily bound or stalled by the logs and breakage of the chain is common. The circular saws, powered hydraulically, can be used under all conditions. The primary drawback of the first type of circular saw described, which only pivots down onto the logs to be cut, is that the width of the cradle is limited by the size of the blade diameter. Since the blade must extend slightly beyond all the logs to make full cuts, the cradle must have a width smaller than the diameter of the blade and the depth of the cradle must be kept well below the center of the blade. Because the cradle size is limited, the amount of wood able to be cut with each pass is also limited. To utilize a wider cradle, and thereby increase the amount of wood able to be cut in a single pass, the second type of saw is known. This type of circular uses a jointed mechanism to hydraulically extend the saw blade across the cradle. The multi-jointed arm moves the blade across the cradle with an elbow-like action. Because of this mechanism, the saw blade is readily subject to binding and stoppage, since the multi-jointed arm is not strong enough to counter any shifting of logs against the blade. This forces the blade off-line and results in stoppage, requiring the operator to retract the blade and start over.
It is an object of this invention to provide a circular saw which can be pivoted down onto the logs in the cradle and then moved transversely across the cradle, such that the cradle width can be maximized. It is a further object to provide such a saw in which the blade is moved in a solid and controlled manner, whereby shifting logs will not bind and stop the blade's rotation. It is a further object to provide such a saw where the blade is moved hydraulically by two pistons, one to pivot the blade down from the recessed position and the other to reciprocate the blade across the cradle and back in a strictly linear motion.